1. Field of the Invention
The invention relates to apparatus for ascertaining phase coherency of signals.
2. Description of the Prior Art
Processing devices contained in signal processing systems, such as trackers and jammers contained in a radar system, commonly operate through a central processing unit to perform their various functions on signals detected by a receiver. In the course of their operation, these devices often require, as an input, the characterization of specified signals as to whether they are phase coherent. With the advent of signal processing systems which utilize digital techniques, a marked improvement in the level of performance of these processing devices has been made possible. However, these improved devices cannot perform at a higher level than the accuracy of the signals which they are given to process.
Prior art apparatus for ascertaining the phase coherency of signals processed in analog systems was incompatible with the improved digital processing devices. Prior art apparatus for determining the phase coherency of signals as used in digital systems was adequate provided the rate of phase shift between the signals was sufficiently large. However, when, in these digital systems, the rate of change in the phase shift between the signals was very small, the signals became indistinguishable from signals which were, in fact, phase coherent. Therefore, to realize the promised level of performance of the improved digital processing devices which required knowledge as to the phase coherency of input signals, there was a need for an improved apparatus for ascertaining when signals are phase coherent or when there is an on-going phase shift between signals. The present invention satisfies this need by providing, to an arbitrarily fine level of accuracy, apparatus for determining whether signals are phase coherent.